In a medium bowl combine 1 cup sliced strawberries, soda, lime juice, and sugar. Cover and chill for 1 to 24 hours, stirring occasionally. Slightly crush berries with a muddler or fork. If desired, strain crushed strawberries; discard seeds.
Transfer strawberry mixture to a pitcher. Stir in whiskey. Cover and chill for 15 minutes.
Before serving, slowly pour sparkling wine and sparkling water into strawberry mixture in pitcher; stir gently to mix. Serve in champagne flutes. If desired, garnish with additional sliced strawberries.